electricity

Question 1

which is positive and which is negative; cathode and anode?

Answer 1

cathode - negative

anode - positive

Question 2

what is electro magnetic induction

Answer 2

a change in magnetic field induces an emf that induces current

Question 3

how is magnetic flux measured

Answer 3

weber

Question 4

what is fardays law of Electromagnetic induction

Answer 4

magnitude of induced emf is proportional to the rate of change of flux or E <× Ø1 - Ø 2 / t

Question 5

what is a magnetic field

Answer 5

region where an attractive repulsive force is felt

Question 6

in what direction do magnetic force lines point

Answer 6

north to south

Question 7

what is an electromagnet

Answer 7

current carrying conductor

Question 8

what is a solenoid

Answer 8

a coil whose length is linger than its radius

Question 9

how do you make a solenoid stronger

Answer 9

place a magnetic core in it

Question 10

what direction is a magnetic north pole

Answer 10

anti clockwise

Question 11

what direction is a magnetic south pole

Answer 11

clockwise

Question 12

what will a current carrying conductor experience in a magnetic field

Answer 12

a force perpendicular to current flow and perpendicular to magnetic field

Question 13

what is conventional current direction

Answer 13

postive to negative

Question 14

what happens if a current carrying wire enters a magnetic field parallel to magnetic flow direction

Answer 14

no force acts on it

Question 15

what happens if a current carrying coil is placed in a magnetic field

Answer 15

it turns

Question 16

what is a characteristic of a thermistor

Answer 16

resistence will drop dramatically at a certain temperature

Question 17

what are the two main types of capacitors

Answer 17

an electrilytic capacitor and a parallel plate capacitor

Question 18

what does dielectric mean

Answer 18

non conductive

Question 19

what are 3 factors affecting capacitance in a parallel plate capacitor

Answer 19

distance between plates, permitivity of dielectric material, area of overlap

Question 20

what is lenzs law?

Answer 20

the direction of current caused by electromagnetic induction will be opposite to the direction of the force causing it

Question 21

how do you demonstrate faradays law?

Question 22

what is the purpose of a transformer

Answer 22

to increase or decrease alternating voltage

Question 23

what is the principle operation of a transformer

Answer 23

1. the input voltage (Vin) in the first (or primary) coil creates an alternating current there, which then creates a changing magnetic field in the core.
2. The secondary coil is inside this changing magnetic field and so it creates an emf in the secondary coil (Vout)
   The voltage can either be increased (a step-up transformer) or reduced (stepped down).
3. This is controlled by the relative number of turns in the primary (Np) and the secondary (Ns).

Question 24

what is alternating current

Answer 24

current that reverses direction over a set period of time

Question 25

describe an experiment to show how resistance of an LDR varies with incident light

Answer 25

connect LDR to ohmeter, shine light with verying distances and observe change in resistance on ohmeter

Question 26

what is rectification

Answer 26

conversion of a.c. ro d.c

Question 27

what semiconductor is used for rectofication

Answer 27

diode

Question 28

why is high voltage used to transport electicity efficiently

Answer 28

according to joules law, a) heat generated in wires is proportional to the square of current so b) a low current is needed to reduce heat thus c) a high voltage is used

Question 29

list 4 sources of emf

Answer 29

dry cell, primary cell, secondary cell, mains

Question 30

what is a semi conductor

Answer 30

a MATERIAL with varying resistance

Question 31

what are two common semi conductors

Answer 31

silicon and gerarnium

Question 32

what is valence

Answer 32

amount electrons in an atoms outer shell needed to fill the shell

Question 33

what happens to a semi conductor like silicon when it heats up

Answer 33

a POSITIVE HOLE is left after an electron leaves

Question 34

what is intrinsic conduction

Answer 34

conductivity in a pure semicondunctor material due to factors like HEAT or LIGHT

Question 35

what is doping in semiconductors

Answer 35

adding impurities to increase extrinsic conductivity

Question 36

what is a p-n diode

Answer 36

when P TYPE and N TYPE semiconductor materials are joined to allow CURRENT to flow in ONE DIRECTION

Question 37

what is the depletion layer in a P-N DIODE

Answer 37

a neutral region where the electron holes and electons have filled each other and there no CHARGE CARRIERS

Question 38

what is required for a P-N DIODE to work

Answer 38

for voltage to exceed JUNCTION VOLTAGE that exists in DEPLETION LAYER AND to be connected in FORWARD BIAS

Question 39

what is forward bias

Answer 39

when the POSITIVE TERMINAL is connected to the p-type and the NEGATIVE TERMINAL is connected to n-type

Question 40

what happens if a semicondictor is connected in reverse bias

Answer 40

depletion layer widens, current doesnt flow except for current leakage, diode eventually breaks

Question 41

what unit is current measured in a) forward biased diode and b) reverse biased diode

Answer 41

a) milli amps and b) micro ampls

Question 42

example of material added to a) p-type dope silicone and b) n-type dope silicone

Answer 42

a) boron b) phosphorus